Aqueous paint or coating compositions, such as latex paint compositions, generally exist as an emulsion, where small droplets of polymer are mixed into an aqueous medium, along with pigments and other excipients. When such compositions are disposed onto a surface, the water in the aqueous carrier slowly evaporates, thereby converting the liquid composition to a solid film.
The transition from liquid composition to solid film can be referred to as coalescence. As the water evaporates, the polymer droplets come into closer contact. If the droplets are relatively soft, the emulsion will break down, the droplets will fuse, and a solid film is formed. But if the droplets are harder, the fusing of the droplets may not occur readily. If fusion of the droplets does not occur, the resulting dried material can crack, flake, or pulverize. A coalescing aid can be added to the composition to facilitate the fusing of the droplets and the formation of a continuous film. In this sense, the coalescing aid can be thought of as a temporary plasticizer of the film-forming polymer.
Most film-forming polymers can be characterized by a temperature below which film formation cannot occur readily. The film-forming polymers suitable for use in paint compositions often have a minimum film-forming temperature (MFFT) of around 15-45° C. Thus, in many instances, the temperature of the surface to be coated can be lower than the MFTT for a given film former. In such instances, it can be desirable to include a coalescing agent in the paint or coating composition.
In some cases, 2,2,4-trimethyl-1,3-pentanediol isobutyrate can be used as a coalescing aid, but has the disadvantage of having a high vapor pressure. As a result, its use in paint compositions can be problematic, as organic vapors are released into the environment as the paint dries. Few suitable non-volatile alternatives exist, however.
Thus, there is a continuing need to develop compounds or compositions that can function effectively as coalescing agents, and which have a low VOC content. Further, it may be desirable to make such compounds from renewable feedstocks, such as certain natural oils, so that their manufacture does not further deplete non-renewable petroleum resources.